In the art of electric arc stud welding a stud welding gun usually is connected electrically to a power supply. The power supply provides power for welding and for control functions; and usually the power supply also includes appropriate control circuitry. An example of a power supply for stud welding is disclosed in U.S. Pat. No. 4,241,285, the entire disclosure of which hereby is incorporated by reference.
The stud welding gun usually includes a chuck into which a stud may be placed, a spring for normally urging the chuck and stud to an extended position with the stud engaging the workpiece, and a lifting solenoid capable of energization to pull in the solenoid armature to move the chuck and stud against the force of such spring thereby lifting the stud from a workpiece to which it is intended to be welded. Ordinarily during use of such a stud welding gun and power supply, the stud is placed into engagement with a workpiece to which it is to be welded; electrical power is provided to effect welding; the gun lifting solenoid is energized to lift the stud from the workpiece thereby drawing an electric arc between the stud and the workpiece; the stud and lifting solenoid are maintained in lifted condition or position relative to the workpiece or to a reference position with respect to the gun until adequate heat has been generated by the arc to effect conditioning, e.g. melting or partial melting, of the metal of the workpiece and/or stud for welding; and then the lifting solenoid is deenergized to allow the aforementioned spring to plunge the chuck and stud back toward the workpiece whereupon the stud becomes securely welded to the workpiece. Variations on such stud welding operation, of course, do exist, but fundamentally the aforementioned steps ordinarily are required to perform electric arc stud welding processes.
A problem encountered with prior art stud welding guns and power supplies is the excessive heat that is generated and accumulates in the lifting solenoid. When a stud welding gun is cycled frequently, i.e. used to weld many studs in a relatively short period of time, the lifting solenoid may overheat causing the insulation thereon, for example varnish, to melt. As a result the lifting solenoid may shortcircuit and become inoperable and the melted varnish or other insulation material may damage other parts of the stud welding gun. The gun then would have to be taken out of use for servicing, for example to replace the lifting solenoid and to clean and/or to repair other portions of the gun.